1. Field of the Invention
The present invention relates to thin optical pickup devices (sometimes referred to as slim or ultra-slim optical pickup devices) for writing to and reading from an optical disc such as a CD (compact disc), DVD (digital versatile disc), etc., and relates to optical disc drive apparatuses incorporating such a thin optical pickup device. The invention also relates to optical pickup devices for writing to and reading from an optical recording medium such as a Blu-ray disc (for use in a blue semiconductor laser), HD-DVD, etc., and relates to optical disc drive apparatuses incorporating such an optical pickup device.
2. Description of the Related Art
The following describes the inner workings of an optical pickup device for writing to or reading from an optical recording medium such as a CD, DVD, Blu-ray disc (for use in a blue semiconductor laser), HD-DVD, etc. This optical pickup device is incorporated in an optical disc drive apparatus. The light emitted from a light emitting device such as a laser diode is directed to the objective lens through optical components such as various lenses, a prism, mirrors, etc., and focused onto the optical disc. The return light from the optical recording medium (or optical disc) passes through optical components such as the objective lens, various lens, mirrors, etc. and is received by a photodiode which then converts the optical power (or signal) into an electrical signal. In the optical pickup device, the actuator finely adjusts the position of the objective lens to maintain it at a predetermined distance (or working distance, hereinafter referred to as “WD”) from the surface of the optical disc, which allows the device to reliably write and read a signal to and from optical disc media conforming to various standards, and even relatively low quality discs having an axial runout.
It should be noted that “half-height type” optical pickup devices, which do not belong to the group of thin optical pickup devices, can be designed to have a sufficient distance between the surface of the optical disc and the surface of the objective lens. This eliminates the need to provide a protector member near the objective lens in such a way that its top is higher than the surface of the objective lens.
However, the recent trend toward thinner personal computers, etc. has resulted in a reduction in the distance between the surface of the optical disc and the surface of the objective lens in each optical disc drive apparatus. This means that the objective lens may collide with the optical disc if the focus servo system does not function as intended or if strong external force is applied to the optical disc drive apparatus. In the worst case, the objective lens or the recording surface of the optical disc may be damaged, making it impossible for the pickup device to read a signal from the disc. In order to prevent this, thin optical pickup devices usually include a protector member that protrudes toward the optical disc such that its tip is closer to the optical disc than the surface of the objective lens.
Such a protector member is made of a special POM (polyoxymethylene) material or a special fluorine-based molding resin material having very high surface slipperiness so as not to damage the surface of the optical disc when the protector member comes into contact with it. More specifically, when the protector member contacts the rotating optical disc, material is readily removed from the surface of the protector member by friction without damaging the surface of the optical disc. Further, even if strong external force is applied to the optical disc drive apparatus or the optical pickup device, the high slipperiness of the surface of the protector member causes the member to slide over the surface of the optical disc, thereby preventing damage to the surface of the optical disc. The lens holder is commonly made of a liquid crystal polymer, which allows for accurate molding.
However, conventional thin optical pickup devices such as that described above are disadvantageous in that the protector member is formed of a special POM material or a special fluorine-based molding resin material (as described above), which results in increased material cost and the need for die replacement during the manufacturing process.
It should be noted that the following patent publications disclose techniques related to optical pickup devices. JP-A-2006-18978 discloses a lens drive mechanism in which the lens protector member protrudes more than the objective lens to prevent contact between the objective lens and the optical disc (or optical recording medium) and thereby prevent damage to the surface of the disc. The lens protector member is made of a UV cure adhesive to avoid an increase in cost and allow the lens drive mechanism to have a simple configuration. JP-A-2006-24339 discloses an optical pickup device in which the lens holder includes a plurality of openings in which lens protectors are to be formed. A resin material such as a UV cure adhesive is injected into selected ones of these openings to form lens protectors and adjust the center of gravity of the moving part at the same time. Further, JP-A-2006-99814 discloses a collision preventing device of an optical pickup device in which at least one molded body having a cushioning coating on its top is implanted in the top peripheral surface of the lens holder holding the objective lens.